Effects of oilseed supplements on milk production and quality in dairy cows fed a hay-based diet

The influence of rapeseed (Brassica napus L.) and linseed (Linum usitatissimum L.) on feed consumption, milk yield, composition and fatty acid (FA) profile was investigated in lactating dairy cows. According to a Latin square design, twelve cows were assigned to three experimental settings which received a hay-based diet supplemented with one of the following mixtures: cracked barley (1.0 kg) and cracked maize (0.5 kg) as Control diet (C-diet); full fat ground rapeseed (1.0 kg), cracked barley (1.0 kg) and cracked maize (0.5 kg) as Rapeseed diet (R-diet) and extruded linseed (1.2 kg), cracked barley (1.0 kg) and cracked maize (0.5 kg) as Linseed diet (L-diet). Diet supplemented with rape- and linseed did not affect dry matter intake. As result of the high amount of dietary ether extract R- and L-diet showed higher crude fat intake as compared to the control. Despite the higher intake of crude fat and, in particular, of the polyunsaturated fraction, milk yield and composition resulted similar among treatments. Compared to C-diet, R-diet resulted in milk containing significantly lower amounts of saturated fatty acids (SFA) (60.9 vs 66.9% of total detected SFA) as well as higher amounts of monounsaturated fatty acids (MUFA) (30.6 vs 24.2%). However, R-diet had no effect on polyunsaturated fatty acid content (PUFA). With respect to C-diet, L-diet also significantly reduced the content of SFA (59.8 vs 66.9%) and increased both MUFA (29.1 vs 24.2%) and PUFA (4.7 vs 4.1%) contents. Feeding about 1 kg of whole oilseeds per head per day had no clear effects on milk vaccenic acid and conjugated linoleic acid contents. The inclusion of rapeseed in the diet significantly reduced the content of n-6 FA in the milk, whereas the linseed-supplemented diet significantly increased the content of n-3 FA. In comparison to C-diet, n-6/n-3 ratio was lower in L-diet milk and intermediate in R-diet milk. Feeding lactating dairy cows with oilseeds rich in unsaturated fatty acids (UFA) did not exert any effects on productive performance. Considering the increase in PUFA and the reduction of n-6/n-3 ratio as a desirable enrichment of milk fat for human health, under our experimental condition feeding linseed appears to improve the nutritional value of milk better than rapeseed.